It is sometimes assumed that water supply systems operate in steady-state hydraulic conditions. In reality, these hydraulic conditions are frequently quasi-steady and unsteady due to the stochastic nature of demand, operations of valves, pumps, malfunctioning surge protection devices and occasional bursts. The current drive for managing leakage by reducing and controlling the operational pressure in near real-time might further exacerbate the problem as it introduces hydraulic instabilities. In addition, pump optimisation which includes frequently switching pumps off and on for energy reduction results in sudden changes in hydraulic conditions. This causes an increase in pipe stress and leads to associated fatigue failures. These sudden and gradual hydraulic variations lead to an increased level of bursts and significant cost in terms of fixing pipe failures and civil litigation claims from those suffering related financial loss.
Therefore, it is highly desirable that the ageing pipeline infrastructure is kept under steady state hydraulic conditions to extend service life. This requires that dynamic hydraulic conditions are continuously monitored and analyzed, such that failures or other undesirable events can be promptly identified and repaired or in some other way addressed.
Current industry practice for monitoring hydraulic conditions in water supply networks makes use of monitoring devices that sample at a frequency of one sample every fifteen minutes (referred to in this disclosure as 15 min sampling). These monitoring devices are powered down between sampling periods to minimise the power consumption and extend the battery life. Consequently data acquired using these devices provide only periodic snapshots of the hydraulic conditions which do not capture the dynamic hydraulic behaviour and/or transient and surge events.
Devices that are capable of high-frequency sampling for monitoring pressure transients, such as pressure surges, already exist. Examples are those devices disclosed in U.S. Pat. Nos. 7,219,553 and 7,357,034. These devices capture pre-defined transient events as the sampling rate is increased when an event is detected and the device stores these events in an internal memory. A surge, which is an example of a transient event, is determined by the rate of change (using a gradient detector) and a maximum threshold. The interpretation of the transient events is done by a human operator and it requires the use of specialised engineering skills.
The main drawbacks of the system described in U.S. Pat. Nos. 7,219,553 and 7,357,034 and other surge monitoring devices are:    (i) Only extreme surge events are captured as the acquisition is triggered by absolute values and gradient thresholds. In reality, dynamic hydraulic conditions are stochastic and characterized by a wide range of frequencies and amplitudes. These are omitted by existing devices.    (ii) The assembly of post-factum surge data from multiple locations is significantly hindered as the transients might have dissipated below the established trigger thresholds and not captured. This significantly limits the quality and availability of the captured data for analyzing the surge events and diagnosing failures; and    (iii) The system is mainly deployed in over ground installations as it requires the use of large energy sources (e.g. large solar panels) and of line of sight (GPS) for time synchronization.
Research by the present inventors in the area of hydraulic transients demonstrates that these events have different characteristics, frequency of occurrence, amplitude, shape, rate of change and energy dissipation. Many of these events do not constitute sudden and extreme transients which cause immediate pipe failures. The dynamic hydraulic conditions frequently include low amplitude high-frequency pressure oscillations for which trigger values such as gradient detectors and threshold are not appropriate. Lowering the trigger values would result in continuous sampling with the acquisition of several orders of magnitude more data which existing surge (i.e. transient) logging equipment cannot manage.
The described dynamic hydraulic conditions will not immediately compromise the integrity of a pipeline. Experimental research by the present inventors has demonstrated that such events cause fatigue failures and accelerate fatigue-induced corrosion. Both of these mechanisms contribute to pipe deterioration and burst frequency. Furthermore, the rapid changes in fluid velocity increase the shear stress along the pipe wall which results in the resuspension of sediments and scouring of biofilms. As a result, the dynamic hydraulic conditions also affect the water quality, decrease the residual chlorine and result in discoloration and customers' complaints. These examples illustrate that the definition and characterization of a transient event such as a surge event requires significantly more sophisticated processing and data management routines than the ones described in U.S. Pat. Nos. 7,219,553 and 7,357,034.